1. Field of Invention
The present invention relates to a digital image processing method, and more particularly to a noise suppression method using multiple digital images.
2. Related Art
With the rapid development of digital cameras, the demands for digital images are greatly increased. The digital camera uses a planar photosensitive element to capture an entire image or a square area from an image. Once an exposure is completed, a control circuit transfers charges on a capacitor unit to a next adjacent unit. When reaching the last unit on the edge, the charge signal is transmitted to an amplifier and converted into an electric potential. The above process is repeated until the entire image is converted into electric potentials. The electric potentials are sampled and digitized and then stored in a memory.
However, after a long-time exposure, surface charge fluctuation occurs to the photosensitive element. Due to the charge fluctuation, some noises are produced in the imaging of the digital image. In addition to the exposure time, the increase of the gain of the photosensitive element may also improve the photoreceptive capability of the photosensitive element but result in the charge fluctuation more easily.
Besides the hardware processing, software processing also causes noises. For example, when an edge sharpening process is performed on the digital image, for pixels of different colors that are originally less visible in the digital image, color gradations of the different colors are raised due to the sharpening process, so that particles of different colors appear in the digital image.
Therefore, a lot of camera manufacturers or image processing manufacturers suggest many noise elimination methods in order to improve the quality of the digital image. Most of the noise elimination methods work with digital filtering techniques. For example, the noise elimination may be implemented by a similar color correction or blurring process. Although these methods can reduce the noises in the digital image, the overall imaging quality of the digital image is affected. For example, for the digital image processed by blurring, the difference between pixels of similar colors may be further reduced, but accordingly, the original boundary in the digital image is blurred and cannot be easily recognized.